Q: how can I change the phone number for messaging and FaceTime?

The phone number that you want to change to has to be an iPhone number that is associated with your Apple ID. Most likely, you will have to sign out of FaceTime and iMessages on your iPhone and iPad, then start all over again by activating both apps on the iPhone first. You will have the opportunity to select any of the phone numbers that are associated with your ID in the settings for each app.

This should be helpful. Read the very last part which deals specifically with iOS devices.

iOS and OS X: Link your phone number and Apple ID for use with FaceTime and iMessage

Unable to make or receive FaceTime calls after April 16, 2014

http://support.apple.com/kb/TS5419

Using FaceTime http://support.apple.com/kb/ht4319

Troubleshooting FaceTime http://support.apple.com/kb/TS3367

The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting

http://tinyurl.com/a7odey8

Troubleshooting FaceTime and iMessage activation

http://support.apple.com/kb/TS4268

iOS: FaceTime is 'Unable to verify email because it is in use'

http://support.apple.com/kb/TS3510

Using FaceTime and iMessage behind a firewall

http://support.apple.com/kb/HT4245

iOS: About Messages

http://support.apple.com/kb/HT3529

Set up iMessage

http://www.apple.com/ca/ios/messages/

iOS and OS X: Link your phone number and Apple ID for use with FaceTime and iMessage

http://support.apple.com/kb/HT5538

How to Set Up & Use iMessage on iPhone, iPad, & iPod touch with iOS

http://osxdaily.com/2011/10/18/set-up-imessage-on-iphone-ipad-ipod-touch-with-io s-5/

Set Up Alert Sounds

http://www.quepublishing.com/articles/article.aspx?p=1873027&seqNum=3

Extra FaceTime IDs

http://tinyurl.com/k683gr4

Troubleshooting Messages

http://support.apple.com/kb/TS2755

Troubleshooting iMessage Issues: Some Useful Tips You Should Try

http://www.igeeksblog.com/troubleshooting-imessage-issues/

Setting Up Multiple iOS Devices for iMessage and Facetime

http://macmost.com/setting-up-multiple-ios-devices-for-messages-and-facetime.htm l

FaceTime and iMessage not accepting Apple ID password

http://www.ilounge.com/index.php/articles/comments/facetime-and-imessage-not-acc epting-apple-id-password/

Fix Can’t Sign Into FaceTime or iMessage iOS 7

http://ipadtutr.com/fix-login-facetime-imessage-ios-7/

FaceTime, Game Center, Messages: Troubleshooting sign in issues

http://support.apple.com/kb/TS3970

Unable to use FaceTime and iMessage with my apple ID

https://discussions.apple.com/thread/4649373?tstart=90

iOS 7 allows you to block phone numbers or e-mail addresses from contacting you via the Phone, FaceTime, or Messages

http://howto.cnet.com/8301-11310_39-57602643-285/you-can-block-people-from-conta cting-you-on-ios-7/

How to Block Someone on FaceTime

http://www.ehow.com/how_10033185_block-someone-facetime.html

My Facetime Doesn't Ring

https://discussions.apple.com/message/19087457#19087457

How to watch FaceTime calls on the big screen with Apple TV

http://www.imore.com/daily-tip-ios-5-airplay-mirroring-facetime

Send an iMessage as a Text Message Instead with a Quick Tap & Hold

http://osxdaily.com/2012/11/18/send-imessage-as-text-message/

To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8

How to Text on the iPad

http://ipad.about.com/od/ipad_tricks/a/How-To-Text-On-The-Ipad.htm

How to Send SMS from iPad

http://www.iskysoft.com/apple-ipad/send-sms-from-ipad.html

How to Receive SMS Messages on an iPad

http://yourbusiness.azcentral.com/receive-sms-messages-ipad-16776.html

Apps for Texting http://appadvice.com/appguides/show/apps-for-texting

You can check the status of the FaceTime/iMessage servers at this link.

http://www.apple.com/support/systemstatus/

 Cheers, Tom